Portable terminal devices, such as portable telephones and personal digital assistants (PDA), having a multi-task operating system (OS) have recently increased. Among such portable terminal devices are devices to which can be added, software whose functions, user interface expression capability, and operability are improved (also referred to as a “rich client”). These portable terminal devices have various functions in addition to making calls. The portable terminal devices offer various functions to the user by executing applications related to email, Web browser, news, viewing of blogs and the like, maps, traffic information, and games, for example.
In portable terminal devices providing various functions such as those above, power consumption increases accompanying increases in the number of functions the device provides. For example, a smart phone is an example of the portable terminal device that has a multi-task OS, and smart phones consume a large amount of power. The functions provided by smart phones include a function that consequent to processes regularly executed such as the reception of email and the updating of resource description framework site summary (RSS) causes the hardware and the software of the portable terminal device to be executed even when the user is not operating the portable terminal device. Such functions further increase the power consumption of the portable terminal device.
A technique has been disclosed that involves estimating the time point of arrival of a packet and based on the estimated time point of arrival, switching the state from an active state of unlimited use of power to a low power state, or from the low power state to the active state, to reduce power consumption (see, e.g., Japanese Laid-Open Patent Publication No. 2002-185475).
Another technique has been disclosed that involves setting the transmission cycle of a beacon signal transmitted by a base station, based on a setting request requested by a terminal station in a wireless communication system, to reduce power consumption. According to this technique, the terminal station causes the check interval of the email application executed by the terminal station and the transmission cycle of the beacon of the base station to coincide. Consequently, the termination station is able to turn off the power supply to the communication circuit until the time when the beacon signal is to be received, enabling reduced power consumption (see, e.g., Japanese Laid-Open Patent Publication No. 2005-130436).
However, according to the conventional techniques, the amount of data transmitted and received by the portable terminal device is estimated based on the result of observation. Therefore, when a large amount of data occurs, a problem arises in that the power consumption of the device increases. According to the technique disclosed in Japanese Laid-Open Patent Publication No. 2002-185475, applications providing various functions do not always operate as expected by the portable terminal device, or one application may operate independently from other applications, resulting in increased power consumption.
According to the other conventional technique, assuming that a transmission process by the base station is “application 1” and a checking process of an email application by the terminal station is “application 2”, this conventional technique is applicable to a portable terminal device and the application 1 can be operated in conjunction with the operation of the application 2. However, a problem arises in that, even if the applications 1 and 2 are associated with each other, power consumption may be affected by the operation of other applications and may not be reduced sufficiently as a result.